A student activity that focuses on the determination of four triazines (atrazine, propazine, simazine and terbuthylazine) in seawater samples using High Performance Liquid Chromatography with Ultraviolet Detection (HPLC-UV) is presented. During the laboratory sessions students learn both the use of the instrument and the principles of chromatographic measurements by testing several mobile phases and applying the optimized method to the analysis of surface waters. Additionally, this project allows students to practice and develop a number of skills including solution preparation, solid phase extraction (SPE) and sample concentration procedures. This laboratory experiment is suitable for both analytical chemistry and environmental sciences and the use of this method as an undergraduate experiment permits to introduce concepts of green chemistry.